It is known to subject kegs that have been returned to beverage manufacturers, such as to breweries, to exterior and interior cleaning procedures that include treatment steps. Known methods include cleaning a keg's interior with different treatment media heated to different treatment temperatures. For example, one method begins with a preliminary treatment with mixed water still containing beverage residues at a treatment temperature of between 50° C. and 70° C. This is followed with alkali and acid at a treatment temperature of between 60° C. and 80° C. Finally, there is a treatment with fresh or hot water at a temperature of some 85° C. Providing different treatment media at different temperatures consumes a great deal of energy.